Nitrous oxide-oxygen nanalgesia is widely employed in dental practice for the relief of anxiety and pain. It has been hypothesized that nitrous oxide-induced analgesia results from release of brain endorphins and activation of opiate receptors. We intend to examine the influence of various concentrations of nitrous oxide-oxygen for different periods of time upon regional brain levels of Beta-endorphin, methionine-enkephalin and leucine-enkephalin, as determined by radioimmunoassay of brain tissues. We also intend to examine whether nitrous oxide induces release of these endorphins by asaying for the presence of these three endorphins in fractions collected from ventricular-cisternally perfused rats during exposure to various concentrations of nitrous oxide-oxygen. We also intend to ascertain whether certain nonnarcotic drugs employed in dentistry might interact with nitours oxide-induced endorphin release; drugs to be tested will include acetylsalicylic acid, chloral hudrate and diazepam. These preliminary experiments will help clarify the pharmacological mecahnism of action of nitrous oxide and will also serve as a first step towards and continuing research interest on the part of the investigators in elucidating the pharmacology of nitrous oxide and the relationship between brain endorsphins, opiate receptors and dental pain.